Acts of Union 1800

The Act of Union 1800 (German Vereinigungsgesetz) was actually two bills passed by the parliaments of the Kingdom of Great Britain (Union with Ireland Act 1800, passed on 2 July 1800) and the Kingdom of Ireland (Act of Union (Ireland) 1800, passed on 1 August 1800). The substance of the two Acts was the state union of the two kingdoms to form the United Kingdom of Great Britain and Ireland, which came into force on 1 January 1801.

The Treaty provided that the hitherto independent Parliament of Ireland was dissolved and that Irish MPs were to be added instead to both Houses of the existing Parliament of the United Kingdom at the Palace of Westminster. In place of the Irish House of Lords, four Bishops of the Church of Ireland and 28 Representative Peers to be elected from the ranks of the Peerage of Ireland were sent to the British House of Lords. Instead of the Irish House of Commons, 100 Irish MPs were henceforth sent to the British House of Commons, which had a total of 658 MPs. This was significantly fewer MPs than Ireland's share of the total population of the new Kingdom of Great Britain and Ireland, which at the time was about one third. Part of the treaty included Catholic emancipation, although it was not included in the text of the Act, as major protests from Irish Protestant opposition were feared. However, because of the faith of King George III, no further action was taken, as this would have violated his oath taken at his coronation.

As the flag of the new kingdom, the Union Jack was supplemented by the St. Patrick's Cross for Ireland.